2002 Es300 Cannot Select Am Band

[LexCal]

I have a 2002 ES300 with Nav/Audio (Mark Levinson). Selection for audio function, FM/AM/Disc/Tape is via a physical button located on the LCD frame. Recently, the AM selection button has stopped working and I can no longer enter the AM radio function.

The button has not completely failed, the unit responds in some fashion to button pushes but it is not to select the AM radio. The response I see is when I am in one of the FM modes (FM1, FM2 or FM Type) and have the nav map screen displayed- when I push the AM selection button in one of these modes the unit responds by displaying the banner identifying current mode and station (the same banner displayed when entering that FM mode via the FM selector button). It does not change the mode.

The AM selection button has no response when in Disc mode and has no response when viewing the Audio setup screen.

Has anyone else observed this behavior?

Is there a fix short of replacing the whole unit?

Thanks